PORTLAND -- Appearing on NBC's Today Show in a preview to a Dateline report, Kyron's mom and her husband, Tony Young said they believe Terri was without a doubt responsible for Kyron's disappearance and had been plotting it for a long time.

I think it was very planned, [ahead of time?] oh yeah, Desiree Young said.

The mother of missing seven-year-old Kyron Horman said she believes there were warning signs before her son's disappearance that she didn't take seriously enough, and now that's haunting her. Young said she has been suffering extreme maternal guilt for not paying attention to what she now thinks were red flags about her son's relationship with his step-mother, Terri Moulton Horman.

Kyron became increasingly unhappy about not spending time with me. He wanted to come and live with us. Several times, he would just break down and just sob because he wanted to stay.

Desiree lives more than four hours away from Kyron, in Medford. Kyron would visit often, as part of her divorce agreement with Kaine Horman. She said it was not only Kyron's actions, but Terri's unusual recent behavior that caused her to suspect something was wrong.

Tony Young also suspicious

Desiree's husband Tony Young, a law enforcement officer himself, said Terri Horman seemed defensive from the very beginning but he didn't begin to question it right away.

Young recalled meeting at the Horman's home near Skyline Elementary within hours of Kyron's disappearance. He'd already been told by the FBI and Multnomah County sheriff's detectives that he would not be given inside information about the case.

But because of his background as a detective in Medford, he felt compelled to the other parents how the investigators would proceed.

I explained to each person that now our lives are not private any more, that the investigators are going to talk to us, that they're going to want to know very detailed information about our lives, that our job is to give that and assist with the investigation and give them as much as they need, Young recalled.

The conversation took place even as search dog teams were scouring the property around the school and volunteers were mobilizing to look for Kyron through the night. Young said he tried to reassure everyone, but Terri protested.

I told everybody there, this is normal. This is what happens. She [Terri] instantly started to express some displeasure with that and not wanting...feeling like she was persecuted. And I thought that was an unusual reaction that early in that, he said. But I didn't act on that, I just thought that was kind of strange. But of course thought about it later, a period of time later, and it started adding up from there.

Court documents have since revealed Terri had already allegedly tried to hire their landscaper to kill her husband.

Desiree disgusted by sexting revelation

Most recently, court documents stated that Terri had been sexting and having an affair with a high school classmate of Kaine's, Michael Cook during the time that searchers were looking for Kyron. Desiree called that disgusting.

I guess, to say it tactfully, it goes to someone's character, Desiree said.

More: Court documents reveal alleged sexual affair

Kaine recently filed contempt of court charges against her after filing for divorce and a restraining order. The contempt of court documents accused Terri of showing the restraining order to Cook, although it was supposed to remain sealed. The court documents also spelled out specific details about her alleged affair with Cook.

In addition, the court documents quoted a gym worker who told police that Terri tried to abduct her 19-month-old daughter from a gym daycare while she thought Kaine was working out.

Responding to those allegations against Terri, Desiree told NBC She's got some guts, I'll give her that. Now's not a good time to be doing stuff like that but, I guess I don't expect anything less.

More: Gym worker warned police about Terri

Kyron has been missing since June 4. Terri told police that she left him at Skyline Elementary School after a science fair and he was walking toward his classroom when she last saw him. Police have never called her a suspect or a person of interest, although much of the investigation has focused on her.

Complete coverage: Kyron Horman's disappearance

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